This invention relates in general to a fluid actuator that includes a hollow cylinder having a piston assembly supported for sliding movement therein. In particular, this invention relates to an improved structure for retaining a piston assembly in position relative to a cylinder, such as during assembly, shipment, or maintenance.
A fluid actuator is a well known device that is responsive to the physical movement of an input member for generating a flow of pressurized fluid to a hydraulically driven output device. A basic fluid actuator includes a hollow cylinder having a piston supported for sliding movement therein. The outer circumferential surface of the piston sealingly engages the inner circumferential surface of the cylinder so as to divide the interior of the cylinder into first and second chambers. A rod is usually connected to the piston for movement therewith so as to define a piston assembly. The rod extends through the first chamber and outwardly from the cylinder so as to function as the input member of the fluid actuator. The second chamber of the cylinder is filled with a hydraulic fluid (typically a relatively incompressible fluid, such as oil or water) and communicates through a fluid conduit with the hydraulically driven output device. When a force is applied to the rod extending from the first chamber, the piston assembly is physically moved relative to the cylinder. As a result, pressurized hydraulic fluid flows through the fluid conduit to the hydraulically driven output device to operate same. Fluid actuators of this general type are commonly used in a variety of applications.
One well known application for such a fluid actuator is in the braking system of a vehicle. In such a vehicular braking system, the rod of the piston assembly is connected (either directly or through a mechanical linkage) to a brake pedal located within the driver compartment of the vehicle, while the hydraulically driven output device communicating with the cylinder is a brake assembly located at the wheel of the vehicle. When a force is applied to the brake pedal by the foot of a driver, the rod and the piston are physically moved relative to the cylinder. As a result, pressurized hydraulic fluid flows through the fluid conduit to the brake assembly to slow or stop rotation of the wheel.
In the manufacture of such vehicular brake assemblies and other types of fluid actuators, it is known to manufacture and assemble the mechanical components of the system in a first location, then transport such mechanical components to a second location for installation on the vehicle. When this is done, it is common for the hydraulic fluid to be provided within the second chamber of the cylinder only after arrival at the second manufacturing location, where the mechanical components of the system are installed on the vehicle. In these instances, it has been found that the piston assembly is able to move somewhat freely relative to the cylinder because both of the first and second chambers of the cylinder are empty during transportation from the first manufacturing location to the second manufacturing location. Such relative movement, if not restrained, can result in undesirable relative movements and impacts between the piston assembly and the cylinder, which can cause damage to the components of the fluid actuator. Similarly, such undesirable relative movement can occur during maintenance of a hydraulic system including the fluid actuator, during which the second chamber of the cylinder is initially drained of hydraulic fluid, then re-filled. Additionally, it is sometimes desirable to retain the piston assembly during installation of a hydraulic brake system. For example, to facilitate the installation process and for safety reasons, it is commonly known to retain the piston assembly relative to the cylinder during the evacuation and fill process of a vehicular braking system during assembly of an automotive vehicle.
In these and other situations, it is known to provide a structure for retaining the piston assembly in position relative to the cylinder to prevent the piston and the rod from moving freely relative to the cylinder. Although known piston assembly retaining mechanisms have been effective, they have been found to be somewhat difficult and time consuming to install and remove. Thus, it would be desirable to provide an improved structure for retaining a piston assembly in position relative to a cylinder that is relatively quick and easy to install and remove.